This invention relates to magnetic bubble domain packages, and, more particularly, to a magnetic bubble domain chip package in which the chip is external to the drive field coil assembly and the bias field is supplied by an open magnet assembly which produces an extremely uniform magnetic field while shielding the chip from stray magnetic fields external to the package.
As is well known in the art, magnetic bubble domain chips require two magnetic fields for proper operation. The first is a bias field which is essentially perpendicular to the surface of the magnetic bubble domain chip, the strength of this field controlling the size of the magnetic bubble domains on the chip. This field must be kept at a precisely uniform strength to keep the magnetic bubble domains at all points on the surface of the chip both the same size and in a non-volatile state. The other magnetic field is a rotating magnetic field which is produced in the plane of the magnetic bubble domain chip surface and which controls the movement of the magnetic bubble domains along the propagation and logic paths disposed on the surface of the chip.
The surface of a conventional magnetic bubble domain chip is composed of magnetizable material which has regions with magnetically easy directions of polarization essentially perpendicular to the planar surface of the chip. As the bias field strength is increased, these regions shrink to form the small localized regions of polarization known as magnetic bubble domains. Further increase in this field strength will further shrink the magnetic bubble domains and eventually make them unstable. The strength of the perpendicular magnetic bias field is thus of significant importance and a precise bias field strength is required to maintain the magnetic bubble domains at the proper size and in a non-volatile state. Stray magnetic fields in the operating environment of the magnetic bubble domain device could alter this field strength and adversely affect the proper operation of the device. Shielding of the magnetic bubble domain chip is therefore required, but this presents a problem in that convenient electrical access to the magnetic bubble domain chip must be acquired through the shielding means. It is also desirable to design a package which may be inexpensively assembled in a mass production environment while providing the packaging requirements unique to magnetic bubble domain devices.
One technique of controlling the movement of the magnetic bubble domains on the chip is to supply the aforementioned layer of magnetizable material on the surface of the magnetic bubble domain chip which supports the bubble domains with an overlay pattern of magnetic material along which the bubble domains are propagated. Propagation is achieved by means of the aforementioned rotating magnetic drive field in the plane of the magnetizable material. As this rotating drive field is re-oriented in its cycle of rotation, a bubble will be propagated along the overlay pattern on the surface of the chip. Provision of this rotating magnetic drive field is a significant problem in the packaging of the magnetic bubble domain chips. One method of providing the rotary magnetic field is to first wind an insulated electrically conductive coil around the chip and then to wind a second electrically conductive coil around and in orthogonal relationship to the first. These coils are then driven by electrical signals which are 90.degree. out of phase with respect to each other, thus producing a rotating magnetic field in the plane of the bubble supporting magnetizable material of the magnetic bubble domain chip located inside the coils. A disadvantage of this scheme is that input and output leads to and from the magnetic bubble domain chip must pass through the coils, thus requiring the coils to be larger than is necessary for the production of the drive field. Larger coils require more power, and the location of the magnetic bubble domain chips within the coils presents a further disadvantage in that a limit to the number of chips which can be packaged is automatically set.